Influence of Salinity on Growth and Physiology of in Vitro Grown Cucumber (Cucumis Sativus L. )

Growth and physiological traits of cucumber (Cucumis sativus L. ) were studied under salt stress in vitro. Microshoots were grown on Murashige and Skooge (MS) solid proliferation media containing 2. 89 μM GA3. Salinity was induced by incorporating 0. 0, 50, 75, or 100 mM of NaCl to the culture media. Microshoots were exposed to direct and gradual shock of salinity. Gradual salt shock was induced by gradually transferring microshoots every week to different NaCl concentration from 0. 0 to 50 to 75 to 100 mM (starting from the control and ending with 100 mM NaCl). Growth parameters (shoot length, fresh shoot weight, dry shoot weight, root length, and root number) were generally reduced with elevated salt level in the direct and gradual salt shock. This reduction was less impaired in the gradual salt shock treatment. Root length was enhanced at 50 mM NaCl in both salt shock treatments. Leaf osmotic potential was significantly reduced (more negative) with increasing salinity. Na concentration was increased in salinized microshoots, K and Ca were reduced with elevated salinity and this reduction was less pronounced in the gradual salt shock. Increasing salt stress significantly reduced N to similar levels in the direct and gradual salt shock treatments. K/Na ratio decreased in salinized microshoot as compared with control and gradually microshoot showed higher K/Na ratio than directly salinized microshoot. Increased NaCl level slightly increased P and Mg concentration in the gradually salinized microshoots and significantly decreased P and Mg concentration in the directly salinized microshoots. Increasing salinity increased ash percent and reduced soluble protein percent, fat, and fiber in microshoots under both salt shocks. Moisture percent significantly decreased in directly salinized microshoots whereas it was maintained constant in gradually salinized microshoots. Carbohydrates content decreased at 50 and 75 mM NaCl, but increased at 100 mM NaCl. Elevated salinity significantly reduced microshoot crude protein content and increased proline and reducing sugars content. Microshoots accumulated higher moisture, reducing sugars, soluble protein, crude protein, proline and lower fat and carbohydrates when gradually salinized than when directly exposed to salt stress